1. Field of the Invention
The present invention relates to a self-locking threaded fastening assembly.
2. Discussion of Prior Art
Conventional threaded fasteners may comprise a nut and a corresponding threaded portion on e.g a bolt or a threaded stud which can be used to fasten components. The nut may be locked on the bolt by means of a split pin. If further security is required, one earlier form of fastening includes a sprung locking ring provided on the bolt, which is permanently located in a groove between the thread and a plain portion of the shank of the bolt. On fitment, the split sprung ring depresses so that it sits flush with the shank diameter whilst the bolt is pushed through the bolthole until it appears on the opposite side. Once the bolt has been inserted, the split sprung ring opens out, preventing the bolt from being retracted through vibration or rotational mechanical actions. A nut is then fitted onto the bolt and where yet more security is required, e.g. for flying controls of an aircraft etc, a split pin would also be fitted. Even if the nut and split pin fail in service, the locking function exerted by the spring locking ring remains.
In practice the component stack may be too wide due to a build up of tolerances, resulting in a need for a bolt of alternative length. This replacement can be costly and time consuming as several components may need to be stripped down and rebuilt. Allowing for the difference in widths of component stack and length of the bolt can also have repercussions for other aspects of the design.
U.S. Pat. No. 5,393,183 shows an assembly having a captive nut and an internally threaded nut but is non-adjustable and requires various bolt lengths in order to satisfy various stack situations. U.S. Pat. No. 3,638,980 shows a self-retained bolt assembly but is also non-adjustable and ones of different sizes would have to be manufactured to deal with different size component stacks.
GB 2340909 discloses a nut and bolt locking system having a washer made of a resilient material. However, the spring lock can be manually pushed back to allow the nut to be removed, which means that it could come loose or be taken apart by unauthorised personnel. GB 1006102 discloses a locking device with a bolt having a helical thread, which can still result in similar problems to those described for the other known devices.
An object of the present invention is to provide an alternative form of self-locking fastening assembly, and preferably one which allows fixing of component stacks of variable width. In a preferred embodiment, the assembly and removal of the fixing means can be achieved using existing tools.
According to a first aspect of the present invention there is provided a self-locking fastening assembly including:
a male member having a shank, the shank including at one end region a helical threaded portion and further including a plurality of non-helical locking grooves located on the shank adjacent or inboard of the threaded portion;
a locking ring which in use is deformed on compression thereof so that its inner diameter contracts such that it can locate in and be retained by one or more of said locking grooves; and
a nut for engaging said threaded portion and applying compression to said locking ring.
The provision of a plurality of locking grooves means that the locking device may be used with stacked components where the stack dimension varies, whilst still providing a good xe2x80x9ctightxe2x80x9d connection.
Preferably, the locking ring is of substantially dished or frusto-conical shape.
The fastening assembly may further include a reaction washer, the reaction washer being located in use on the shank adjacent the locking ring. The reaction washer is preferably at least partially tapered or frusto-conical in shape, and in use the inner diameter of the reaction washer preferably abuts the inner diameter of the locking ring.
Preferably, the nut has a receiving cavity at one end defined by an outer circumferential lip, the receiving cavity having such dimensions that the locking ring can be at least partially contained within it. Normally, when the fastening assembly is assembled, the outer diameter of the locking ring abuts the receiving cavity. In use, the lip of the receiving cavity preferably abuts the reaction washer, thereby allowing the clamping force exerted by the nut to be transmitted to the washer, and not just the locking ring, when the nut is tightened.
The fastening assembly may further include at least one spacing washer arranged in use inboard of the reaction washer.
The male member may be a bolt or a threaded stud.
Whilst the invention has been described above, it extends to any inventive combination of the features set out above or in the following description.